svoid wmctrl_closeWindow(wmctrl_Entry e) {
  if (e != null) wmctrl_closeWindow(e.windowIdentity);
}

svoid wmctrl_closeWindow(S windowIdentity) {
  if (nempty(windowIdentity)) backtick("wmctrl -i -c "
    + assertRegexp("0x[a-fA-F0-9]+", windowIdentity));
}